US6537135B1 - Curvilinear chemical mechanical planarization device and method - Google Patents

Abstract

The present invention relates to an apparatus and method for polishing substrate surfaces. The method can include the steps of holding a substrate against a polishing surface and depositing slurry on the polishing surface. The method can further include the step of moving the holding device in a substantially curvilinear path relative to the polishing surface, or the step of moving the polishing surface in a substantially curvilinear path relative to the holding device. The apparatus comprises a polishing surface, a holding device for holding a substrate against the polishing surface, and a slurry supply system for depositing slurry on the polishing surface. The apparatus further includes a moving structure for moving the holding device in a substantially curvilinear path along the polishing surface, or a moving structure for moving the polishing surface in a substantially curvilinear path relative to the holding device. The substantially curvilinear path is preferably substantially a figure eight path.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

(Not Applicable)

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

(Not Applicable)

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the field of semiconductor wafer fabrication, and more particularly to the field of chemical mechanical planarization (CMP) of thin films used in semiconductor wafer fabrication.

2. Description of the Related Art

The production of integrated circuits begins with the creation of high quality semiconductor wafers. A semiconductor wafer typically includes a substrate, such as a silicon or gallium arsenide wafer, on which a plurality of transistors have been formed. Transistors are chemically and physically formed in and on a substrate by patterning regions in the substrate and patterning layers on the substrate. The transistors are interconnected through the use of well known multilevel interconnects to form functional circuits. Typical multilevel interconnects are comprised of stacked thin films, commonly comprised of one or more of the following: titanium (Ti), titanium nitrite (TiN), tantalum (Ta), aluminum-copper (Al—Cu), aluminum-silicon (Al—Si), copper (Cu), and tungsten (W).

During the wafer fabrication process, the wafers may undergo multiple masking, etching, dielectric deposition, and conductor deposition processes. An extremely flat, or planarized, surface is generally needed on at least one side of the semiconductor wafer to ensure proper accuracy and performance of the microelectronic structures being created on the wafer surface. In general, a wafer can be polished to remove high topography, surface defects such as crystal lattice damage, scratches, roughness or embedded particles. As the size of integrated circuits continues to decrease and the density of microstructures on an integrated circuit continues to increase, the need for precise wafer surfaces becomes more important. Therefore, between each processing step, it is usually necessary to polish the surface of a wafer in order to obtain the most planarized surface possible.

CMP is routinely used to planarize the surface of the layers, or thin films, of the wafer during the various stages of device fabrication. CMP has emerged as the planarization method of choice because of its ability to planarize better than traditional planarization methods. During a CMP process, polishing planarizes surfaces to very precise tolerances, which is essential for maintaining the precise photolithographic depth of focus required for integrated circuit chip fabrication. In a typical CMP process, the wafer is held by a rotating carrier with the active wafer surface facing a rotating polishing table, called a platen. On top of the platen is a porous polyurethane polishing surface on which is poured a slurry. The slurry can be colloidal silica suspended in an aqueous solution. Slurries with different chemical compositions are used to polish metals and other films. During metal polishing, the slurry chemically reacts with the wafer's surface, forming a passive layer on a portion of the wafer's surface, while the mechanical force exerted by the pad and the colloidal silica particles abrades the wafer's surface, removing the passive layer.

A CMP slurry serves several functions. Most notably, it is the medium in which abrasive particles are dispersed. Additionally, it furnishes the chemical agents which promote the chemical process. To obtain optimum results from CMP processing, there must be a synergistic relationship between the chemical and mechanical processes.

For example, CMP slurries for polishing a metal layer commonly comprise a metal oxidizer and an abrasive agent. The oxidizer reacts with the metal to form a passive metal oxide layer. During the polishing process, the abrasive agent removes the passive oxide layer from elevated portions of the metal layer. Depressed portions of the metal layer surface are not subjected to mechanical abrasion and, therefore, the protected material underlying depressed portions of the passive oxide layer is not polished. This process continues until the elevated portions of the metal layer have been polished away, resulting in planarization.

The ideal polishing process can be described by Preston's equation: R=K_p*P*V, where R is the removal rate, P is the applied pressure between the wafer and the polishing surface, V is the relative velocity between the wafer and the polishing surface, and K_pis a function of consumables such as polishing surface roughness, elasticity, and chemistry. The ideal CMP process has constant pressure between the polishing surface and the wafer, constant polishing surface roughness, elasticity, area, and abrasion effects, and constant velocity over the entire wafer surface. Having constant velocities at points which are distant from the center of the wafer is generally preferable to having fluctuating velocities because the removal rate is much easier to control when constant velocity conditions exist. For example, when points at a distance from the center of the wafer are exposed to alternating high and low velocities, the abrasive material may scratch the surface of the wafer and result in a non-planarized surface. Non-uniform removal of films from the surface of a wafer is a common problem encountered during CMP processing because there are numerous variables which can affect planarization.

In a typical CMP process, the wafer carrier and the platen rotate in the same direction, but with the two rotating axes offset by some distance. This arrangement results in relative linear motion between any position on the wafer and the polishing surface. Thus, removal caused by the polishing surface is related to the radial position of the wafer relative to the platen. The removal rate increases as the wafer moves radially, or linearly, outward relative to the platen. Removal rates tend to be higher at the edges of the wafer than at the center of the wafer. As a result, wafer surfaces tend to become higher at the center of the wafer as compared to the edges of the wafer. Reducing this center-to-edge variation results in a more planarized wafer surface.

Attempts have been made to reduce this center-to-edge variation by polishing in non-linear polishing patterns. One approach includes affixing a mechanical template having a non-linear opening to a polishing surface. A rotating motor moves a wafer carrier along the edges of the non-linear template, allowing the wafer carrier to traverse the surface of the polishing surface in a non-linear manner. This approach is significantly limited, however, because it requires attaching a device to the polishing surface. Such a configuration can significantly reduce the polishing surface lifespan by causing uneven wear of the polishing surface. The direct contact between the template and the polishing surface also reduces the lifespan of the polishing surface because the template can introduce particles and other defects into the polishing surface. Another approach involves the use of a non-linear carrier displacement mechanism for moving a wafer carrier across a polishing surface. A drawback to this configuration is that it does not provide a means for moving a wafer across a polishing surface along a substantially figure eight path.

SUMMARY OF THE INVENTION

The present invention relates to an improved apparatus and method for planarizing the surface of a substrate, such as a semiconductor wafer. In one embodiment of the invention, the apparatus for polishing substrate surfaces includes a polishing surface, a holding device for holding a substrate against the polishing surface, a slurry supply system for depositing slurry on the polishing surface, and structure for moving the holding device in a substantially figure eight path relative to the polishing surface. The moving structure can comprise a motor and an actuating arm connecting the motor to the holding device.

In another embodiment, the apparatus for polishing substrate surfaces includes a polishing surface, a holding device for holding a substrate against the polishing surface, a slurry supply system for depositing slurry on the polishing surface, and a structure for moving the holding device in a substantially curvilinear path relative to the polishing surface. In this embodiment, the moving structure can include a drive which is attached to the holding device, structure for rotating the drive, and at least one steering device for steering the drive in a substantially curvilinear path relative to the polishing surface. The substantially curvilinear path can be a substantially figure eight path. The steering device can be one or more cams.

Yet another embodiment of the invention comprises a polishing surface, a holding device for holding at least one substrate against the polishing surface, a slurry supply system for depositing slurry on the polishing surface, and a moving structure. The moving structure can include a drive which is attached to the holding device and rotates the holding device, and counter-rotating devices having structure for engaging the holding device. The counter-rotating devices alternately engage the holding device, thereby moving the holding device in a substantially curvilinear path relative to the polishing surface. The substantially curvilinear path can be a substantially figure eight path.

A method for polishing substrate surfaces according to the invention includes the steps of holding a substrate against a polishing surface with a holding device, depositing slurry on the polishing surface, and moving the holding device in a substantially figure eight path relative to the polishing surface with moving structure. The step of moving the holding device in a substantially figure eight path relative to the polishing surface can be performed with a motor and an actuating arm connecting the motor to the holding device.

Another method according to the invention includes the steps of holding a substrate against a polishing surface with a holding device, depositing slurry on the polishing surface, rotating the holding device with a drive attached to the holding device, and steering the drive in a substantially curvilinear path relative to the polishing surface with at least one steering device. The substantially curvilinear path can be a substantially figure eight path, and the steering device can be one or more cams.

Still another method according to the invention includes the steps of holding a substrate against a polishing surface with a holding device, depositing slurry on the polishing surface, rotating the holding device with a drive attached to the holding device, providing a plurality of counter-rotating devices having structure for engaging the holding device, and rotating the counter-rotating devices. The counter-rotating devices alternately engage the holding device, whereby the holding device moves in a substantially curvilinear path relative to the polishing surface.

BRIEF DESCRIPTION OF THE DRAWINGS

There are shown in the drawings embodiments which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown, wherein:

FIG. 1 is a side schematic view of a conventional CMP apparatus.

FIG. 2 is a top schematic view of the conventional apparatus of FIG.1.

FIG. 3ais a top schematic view of a curvilinear polishing system showing curvilinear polishing according to the invention.

FIG. 3bis a top schematic view of an alternative curvilinear polishing system showing curvilinear polishing according to the invention.

FIG. 3cis a top schematic view of a curvilinear polishing system showing curvilinear polishing of a plurality of wafers with a plurality of wafer carriers according to the invention.

FIG. 4 is a top schematic view of a curvilinear polishing system with steering devices according to the invention.

FIG. 5 is a side schematic view of the rotating devices of FIG.4.

FIG. 6 is a top schematic view of a curvilinear polishing system with counter-rotating devices according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIGS. 1 and 2, a semiconductor wafer10 is shown pressed against a polishingsurface12, which is preferably a polishing pad. The wafer10 is pressed against the polishingsurface12 by awafer carrier16. In a conventional CMP device, the wafer10 is held face-down by thewafer carrier16. A thin synthetic film (not shown) can rest on the back side of the wafer10. The synthetic film can have small holes through which back pressure may be applied during polishing. The back pressure can be used to prevent wafer bowing during polishing and to improve polishing uniformity.

Thewafer carrier16 is often composed of a material which can damage the wafer10 if it directly contacts the wafer10. Therefore, thewafer carrier16 can be pressed against awafer holder26 which helps protect the wafer10 by separating thewafer carrier16 from the wafer10. Thewafer carrier16 can also be rotated by awafer carrier spindle18, causing the wafer10 to rotate as it contacts the polishingsurface12.

According to conventional CMP processes, the wafer10 is pressed against the polishingsurface12, and aslurry supply system20 appliesslurry24 to the polishingsurface12. During the CMP process, aplaten spindle22 rotates theplaten14, independent of the rotation of the wafer10 and thewafer carrier16. The rotation of theplaten14 and thewafer carrier16 causes the wafer10 to move through theslurry24 in a rotary fashion. Asslurry24 flows over the surface of the wafer10, the suspended particles in theslurry24 and the polishingsurface12 mechanically abrade the surface and the liquid in theslurry24 chemically etches the abraded area. In this manner, a substantial amount of material from the high spots on the wafer10 is removed, while a negligible amount of material from the low spots on the wafer10 is removed, resulting in a flattened, or planarized, wafer10.

FIG. 3ashows curvilinear polishing according to the present invention. Awafer carrier32 presses the surface of a wafer (not shown) against a polishingsurface30. Preferably, thewafer carrier32 can move axially and laterally relative to the polishingsurface30. As thewafer carrier32 moves the wafer across the polishingsurface30, thewafer carrier32 can be rotated by adrive34. Thedrive34 is preferably a flexible rod or a connector that is rotated by a motor (not shown). Thedrive34 can rotate thewafer carrier32 in any suitable manner.

Thewafer carrier32 can be rotated by thedrive34 while thewafer carrier32 moves curvilinearly across the polishingsurface30. Curvilinear paths followed by thewafer carrier32 preferably extend across the diameter of the polishingsurface30. In a particularly preferred arrangement, the curvilinear path traveled by thewafer carrier32 as it moves relative to the polishingsurface30 substantially takes the shape of one or more figure eight paths. An advantage of figure eight paths is that such paths expose the wafer to multiple directions of polishing. Accordingly, although a wafer traversing a figure eight path across the polishingsurface30 may be scratched by the polishingsurface30 as it moves along a first portion of the figure eight path, such abrasions can be removed as the wafer traverses a second portion of the figure eight path. Similarly, wafer surface imperfections not removed as the wafer moves through the first portion of the figure eight path can be removed as the wafer traverses the second portion of the figure eight path.

The substantially figure eight paths may be of any suitable size. For example, the substantially figure eight paths can be large enough to extend across the diameter of the polishingsurface30. Substantially figure eight paths large enough to extend across the diameter of the polishingsurface30 can allow even wear of the polishing surface.

Anactuating arm36 can connect amotor38 to thedrive34. Themotor38 can move thearm36, and thus the attachedwafer carrier32, curvilinearly across the polishingsurface30. Themotor38 can be programmed to move thearm36 in any desirable curvilinear direction, including a substantially figure eight path.

In FIG. 3a,thewafer carrier32 is shown traversing a substantially figure eight path near the center of rotation of the polishingsurface30. As shown in FIG. 3b,however, each substantially figure eight path can begin and end at any point along the polishingsurface30. Additionally, as shown in FIG. 3c,the apparatus according to the invention may utilizemultiple wafer carriers32. Eachwafer carrier32 can independently traverse the polishingsurface30 by following one or more substantially figure eight paths. Eachwafer carrier32 can be moved along the substantially figure eight paths by anarm36 which is connected to amotor38.

In another embodiment of the invention, the wafer can be held substantially stationary against the polishingsurface30, while the polishingsurface30 moves in a substantially curvilinear manner. In this embodiment, any suitable motor (not shown) can be used to move the polishingsurface30 in a substantially curvilinear manner. The substantially curvilinear motion is preferably a substantially figure eight motion.

There are many other ways to impart curvilinear motion according to the invention. FIGS. 4 and 5 show an embodiment in which one ormore steering devices46,48 steer awafer carrier42 across a polishingsurface40 in a curvilinear manner. Thesteering devices46,48 may be any mechanism suitable for steering thewafer carrier42, but preferably are cams. Eachsteering device46,48 can be attached to a motor (not shown) by anactuating arm47,49. The motors and actuatingarms47,49 rotate eachsteering device46,48 about its respective axis. Thewafer carrier42 has adrive44 which rotates thewafer carrier42 about its axis as it traverses the polishingsurface40. Thedrive44 is preferably a flexible rod or a connector that is rotated by a motor (not shown). Thewafer carrier42 is shown pressing thewafer holder52 against the back surface of thewafer54, and thewafer holder52 is shown pressing the surface of thewafer54 being polished against the polishingsurface40.

For this embodiment, the movement of thewafer carrier42 in a substantially curvilinear or a substantially figure eight motion can be caused by two independent motions. For example, this movement can be caused by thewafer carrier42 moving linearly across the polishingsurface40 as indicated byarrows41 and43, while steeringdevices46,48 steer thedrive44 in a curvilinear manner by alternately pressing against thedrive44. Contact between asteering device46,48 and thedrive44 communicates motion to thedrive44, which permits thedrive44 to push thewafer carrier42 relative to the polishingsurface40. The motion communicated to thedrive44 can be dictated by the geometry of the edges of thesteering devices46,48 or the geometry of one or more grooves cut in the edges of thesteering devices46,48. Thesteering devices46,48 can be configured to move thedrive44, and thus the attachedwafer carrier42, along any desirable curvilinear path along the polishingsurface40. As previously indicated, however, it is preferable for this curvilinear path to substantially take the shape of a figure eight.

Another embodiment of the invention is shown in FIG.6. This embodiment includes a plurality ofcounter-rotating devices66,68 which move awafer carrier62 in a curvilinear path relative to a polishingsurface60. Preferably, the curvilinear path is one or more substantially figure eight paths. Eachcounter-rotating device66,68 can be rotated about its axis by adrive70,72. Thewafer carrier62 also has adrive64 which rotates thewafer carrier62 about its axis as it traverses the polishingsurface60. Any suitable motor can provide the rotation of thedrives64,70,72.

Eachcounter-rotating device66,68 has one ormore extension arms74 extending radially outward relative to its center. Preferably, theextension arms74 have amain portion76 and acontact portion78. Eachmain portion76 can be attached to acontact portion78 in any suitable manner. Preferably, themain portion76 is attached to thecontact portion78 by a pin, so that thecontact portion78 can pivot relative to themain portion76. Thecontact portion78 carries thewafer carrier62 as thecounter-rotating devices66,68 move thewafer carrier62 relative to the polishingsurface60.

During operation, thecounter-rotating devices66,68 alternate moving thewafer carrier62 relative to the polishingsurface60. Accordingly, eachcounter-rotating device66,68 can receive thewafer carrier62 in one of itsextension arms74, complete approximately one revolution, and then transfer the wafer carrier to the other of thecounter-rotating devices66,68. Thecontact portion78 of theextension arm74 holding thewafer carrier62 can pivot at least slightly towards or away from themain portion76 of theextension arm74 as thewafer carrier62 is transferred from onecounter-rotating device66,68 to anothercounter-rotating device66,68. Thecounter-rotating devices66,68 allow thewafer carrier62 to traverse the polishingsurface60 along a curvilinear path. Preferably, the curvilinear path is a substantially figure eight path.

It is understood that the embodiments of the present invention are described in the context of devices and methods for polishing semiconductor wafers, although those skilled in the art will recognize that the disclosed devices and methods are readily adaptable for other applications, including polishing of substrates other than semiconductor wafers. It should also be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application. The invention can take other specific forms without departing from the spirit or essential attributes thereof.

Claims (2)

What is claimed is:

1. A method for polishing substrate surfaces, said method comprising the steps of:

holding a substrate against a polishing surface with a holding device;

depositing slurry on the polishing surface;

rotating the holding device with a drive, wherein the drive is attached to the holding device;

providing a plurality of counter-rotating devices having structure for engaging the holding device; and

rotating the counter-rotating devices, wherein the counter-rotating devices alternately engage the holding device, whereby the holding device moves in a substantially curvilinear path relative to the polishing surface.

2. The method according toclaim 1, further comprising the step of rotating the counter-rotating devices, wherein the counter-rotating devices alternately engage the holding device, whereby the holding device moves in a substantially figure eight path relative to the polishing surface.

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